The 'Cosmos' by Carl Sagan is a great step towards of popularization of science. In fact, in the introduction, Carl Sagan says as much that he was trying to find a way to satisfy the curiosity of masses who wanted to know more about the universe. With the recent space missions of United States and Soviet Union including manned moon mission of US, the general public was curious about these topics. 'Cosmos' was made as a TV series and at the same time written as a book, though both were not exact copy of each other. There are few things which are found in thirteen part TV series and not found in the book and vice versa. This book was written for anyone with interest in science without any prerequisites.
The author talks about the developments in science and technology in different ancient civilizations. The author also remembers contribution by Ionian scientists. While talking about these developments, he ponders how the study of stars and planets by these scientists and philosophers helped in development of astronomy and astrology. At that time no difference was made by the people between astronomy and astrology. Astrology was considered to be a true science like alchemy, but in reality it was a pseudo-science. Sagan thinks that whatever was unknown or not deducible was attributed to supernatural powers or God. Certain movements of planets, stars or comets were thought to be inauspicious and were thought to forecast the natural calamities like floods, epidemics, earthquakes and droughts.
Sagan describes later developments in sciences - astronomy, physics, chemistry and biology, of course assisted by mathematics. Sagan talks in detail about how life could have originated on earth and how favorable were the conditions. A molecule managed to duplicate itself and that is how seeds of life were sown on earth. Then complexity of life forms increased with passing time. Nucleic acids developed to store information about the functions of cells. Mitochondrion, which is supposed to have been a different organism altogether, developed as the powerhouse of a cell. Then after billions years of evolution complex organisms like reptiles, mammals evolved and vanished. Evolution is a complex process with uncertain outcomes. Here Darwin’s theory of 'Natural Selection' becomes applicable. Sagan also talks about 'Artificial Selection' where an intelligent species, in our case human, controls and directs the evolution of another species. Example can be given of certain crops which were grown by humans and mutated to increase the yield in such a way that few plants cannot even reproduce by themselves.
Sagan talks about the inner solar system and he presents the scientific discoveries made available by spacecrafts flown near and into these planets. For example, Venus was found to be covered permanently by acid clouds and surface was very deep beneath these clouds. Mars had many craters which can be attributed to low density of atmosphere, which cannot burn completely the meteors. The same can be said about the moon, but although there are many impact craters which can be seen on lunar surface, Sagan calculated that the gap between two successive impacts is thousands of years.
Jovian planets or planets in the outer solar system are very big and have many moons of their own. Jupiter has a dozen or so moons of itself and is around thousand times as big as earth. These planets resemble a mini solar system where satellites revolve around these planets. If Jupiter would have been a little bigger, its gravitational pressure would have caused fusion reaction at its core and it would have been a star much like sun and solar system would have been a dual-start system, much like other star systems in our galaxy. Few of the moons of these planets contains ice, iron etc. and hence, are more habitable than their planets which are just sphere of gases.
This book was published in 1980, when space exploration was only two decades old. At that time, Sagan mentioned many possible projects which could be taken up in future. One example can be given of martian rovers - Curiosity and Opportunity - which have reached Mars and sent useful information. The possibility of sending martian rovers was discussed by Sagan. Another example is that of discovery of water on Mars. I was wondering what would have been the impact of that discovery on speculations of the possibility of life on Mars. Here I think that if this book was written after thirty years it would have given much more information, but then it can be said the purpose of this book was not to be informative but to arouse the curiosity of common reader and reduce the role of the supernatural in cosmos.
Sagan also discusses the possibility of extraterrestrial life. He concludes that size of universe is so big and that we know so little about it that the life on any other planet could not be ruled out. He points out that the common mistake that we make is that we always think life on the other planets to be similar to that of the earth. He says that their origin could be very different from ours. The mutation in the genes could have gone any other way. Many stories, both old and new, could be found about UFOs but none of these could be verified. He says that the nearest planet with earth like conditions is around 200 light-years away and it has not been 200 years since we have started sending radio waves in space. If civilizations on any other planet in universe are more intelligent than us, then they might decode the radio waves. For the purpose of communication with extraterrestrial beings, Voyager space probes were sent with information which if found by intelligent beings in universe could reveal some information about earth.
Like other books in popular science category, for example Stephen Hawking’s Brief History of Time, it depends less on equations and mathematical jargons to explain scientific concepts. This books also serves as the history of science in a way as Sagan invokes many discoveries by scientists of old and new civilizations. Sagan calls the time elapsed between Hypatia of Alexandria and scientists during Renaissance as the lost millennium because very few significant discoveries were done in these thousand years. The last two chapters where Sagan explore the possibility of life anywhere else in universe are little slow but overall, this is an interesting book.